216 



The Journal of Heredity 



pigmentation. This gives the experi- 

 menter further ground for the behef 

 that the formation of pattern on the 

 shell is connected with and influenced 

 by fertilization. 



Assuming for the moment that this 

 conclusion is well founded, that we 

 actually have xenia or something like 

 it in birds, how 

 could it be ex- " 



plained"' Which- 

 ever way we 

 turn, we run 

 against generally 

 accepted princi- 

 ples of biology 

 that we can not 

 avoid: it is this 

 fact as much as 

 the lack of ade- 

 quate experi- 

 mental evidence, 

 no 5 doubt, that 

 makes the aver- 

 age biologist in- 

 credulous about 

 the whole idea. 

 Two p o s si b 1 c 

 means of explain- 

 ing an influence 

 of the male in 

 this connection 

 are suggested by 

 von Tschermak. 

 The first he calls 

 an " intra -oval 

 xenia- reaction," 

 meaning that the 

 effect of hybrid- 

 ization on the 

 egg shell is an 

 effect jjroduced 

 by the embryo 



— that is, in the last analysis, an 

 effect of a single sperm. The second 

 method is "extra-oval xenia-reaction," 

 which supposes that the effect is pro- 

 duced by the influence of the whole 

 quantity of sperms on the matc-rnal 

 uterus. 



The first hypothesis seems to von 

 Tschermak to be simple and acceptable, 

 but most readers will i)robably share 

 the feelings of Walther, who remarks: 



"An influence that goes in a very short 

 time, ])artly through the yolk and always 

 through a surrounding body of un- 

 organized albumen, through the entire 

 shell, and demonstrates its presence on 

 the very outside layer of this shell of 

 lime and — this is a point that I think 

 has not been sufficiently emphasized — 



ONE SOURCE OF ERROR IN I 



Photoj^raph by the Bureau of Animal Industry, U. S. Department of Agriculture, sh( 

 (luring recent years show that the eggs of any individual hen tend to become a 

 believed, is likely to be a dwarf, such as is shown at the right in the above photogr 

 however, the eggs of any individual fowl usually vary only slightly from a certain a 

 matter determined by heredity. But the wide range of variation in weight of egf 

 one who is conducting experiments on the subject make constant use of trap-nests 



only on this outside layer of shell: 

 certainly no one can form even the 

 slightest conception of how such an 

 influence could originate or exert itself." 

 To most biologists, the second hypo- 

 thesis will seem little better. There is, 

 however, a small amount of e\'idence 

 now accumulating,^ which indicates 

 that the sperms which do not play any 

 direct part in reproduction may survive 

 for a time and possibly exert some 



< Sec Kohlbrugge, J. H. F., in Ztschft. f. Morphologic u. Anthropologic, 12 Band, 1910, S. 

 359-368, and in Arch. f. Entwicklungsmechanik, 35 Band, 1912, S. 165-188. 



